Edge holes topology. How to make holes like this?
You can use the extrude function to do this. 

Lets say you have the following mesh:



Now we need to add some extra edge loops to the area want want to extrude. This can be done by clicking CTRL + R.



Once for the top and repeat that for the bottom.



Once for the side. Do this also on the other side



Now we going to Face Select and select the part we want to extrude



Now we can extrude the selected faces by pressing E and dragging it to the position you want.

You can add a few extra edges to it to control the subdivide but I find mostly that its not needed and just creates more vertex.

Result